The n_steps variable corresponds to the number of *pairs* of
texture lookups that the blur shader does. For example, when
n_steps = 1, the for-loop reads 1 pixel before and 1 pixel
after the current one.
Our blur shader is heavily inspired in WebRender's blur shader,
the biggest difference being that we calculate the gaussian
samples in the fragment shader itself, and not in the vertex
shader. (This could be an improvement in performance for the
future though!)
WebRender's blur shader calculates n_steps differently than what
we currently do, though. It calculates n_step in such a way that
at least 2 steps are performed for evey non-zero sigma value.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1646>
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